1. FIELD OF INVENTION
This invention relates to a method and apparatus for fabricating thermoplastic containers, and particularly thermoplastic containers which are nestable in configuration and whose bodies are formed from rectagular blanks of a semi-rigid, heat-shrinkable thermoplastic material by heat-shrinking.
2. DESCRIPTION OF THE PRIOR ART
U.S. Pat. No. 4,072,549 (Amberg, et al), which is assigned to the assignee of this application, relates to a method and apparatus for forming nestable thermoplastic containers, such as drinking cups. Each nestable container which is formed by the method and apparatus of the Amberg et al patent has a body which is formed from a rectangular blank of a semi-rigid, heat-shrinkable material. According to the techniques of the aforesaid Amberg et al patent, cylindrical sleeves are formed from a web of a thermoplastic material at a first station, in an operation in which the web is cut into rectangular blanks before the blanks, in succession, are fabricated into the cylindrical sleeves. The sleeves are then transferred in succession to a second station, which is a rotary turrent that carries a multiplicity of individual forming mandrels. Each forming mandrel is in the shape of the frustoconical cup that is to be formed thereon, with the bottom end of the cup being the top end of the mandrel on the rotary turret of the cup making machine. As the cup forming mandrel turret rotates, the cylindrical sleeves on the madrels thereof are gradually and successively manufactured into cups in a series of operations that includes the feeding of a circular bottom closure disc onto the top of the mandrel, the heating of the cylindrical sleeve to cause it to shrink to conform to the shape of the mandrel and to seal an inturned marginal portion of the sleeve to the bottom closure disc to form a sealed bottom for the cup, and the forming of a rim on the outside of the top end of the cup, which is the bottom end of the cylindrical sleeve in its orientation in the various stations of the rotary turret of the cup-making machine.
Cups of other nestable containers that are produced by means of a cup-making machine of the type described in the aforesaid Amberg, et al patents are generally described in U.S. Pat. No. 3,854,583 to Amberg, et al., which is also assigned to the assignee of this application, and such cups are preferably of a two-piece configuration, in which the cup bottom is formed from a disc-shaped piece of a thermoplastic material that is heat-sealable to an inturned marginal portion of the heat-shrunken cylindrical sleeve to form a bottom seam. However, according to the aforesaid U.S. Pat. No. 3,854,583, the cups may also be formed with an integral bottom from a single piece of a heat-shrinkable material, viz., the rectangular blank that is used to form the container sidewall, by utilizing a blank with a vertical dimension that substantially exceeds the vertical height of the container sidewall, and by heat shrinking and fabricating the excess height of the rectangular blank into the integral bottom of the container, as is taught in the aforesaid U.S. Pat. No. 3,854,583.
In the production of cups or other nestable containers by means of a cup-making machine of the type described in the aforesaid U.S. Pat. No. 4,072,549, it has been found that the productivity of the machine is limited by the rate at which cylindrical sleeves can be formed in the sleeve fabrication device employed at the first station of the machine, since the sleeve fabrication device uses a single winding member for the winding or wrapping of all the cylindrical sleeves for the various forming mandrels on the associated rotary turret of the machine. Inherently, it was found that sleeves could not be fabricated as fast as they could be processed into nestable cups in the subsequent operations of the cup-making machine and, therefore, the output of the machine was found to be less than that which the machine was otherwise capable of producing.
Another productivity-limiting feature of the machine of the aforesaid U.S. Pat. No. 4,072,549, when used to produce two-piece cups, is that the cup bottom pieces are transferred to the cup mandrels after the mandrels have been indexed from the station where the cylindrical sleeves for the cup bodies are applied thereto. No work can be done on the cylindrical sleeves to transform them into cup bodies until after they have been properly positioned with respect to the bottom pieces that they are to be assembled to, and the portion of the cup forming machine that is located between the sleeve transfer station and the bottom disc transfer station is essentially out of production.